1. Field of the Invention
The invention relates to a piston for a hydrostatic piston machine, in particular of swash plate construction having a cylinder drum, axial cylinder bores arranged therein, and a swash plate on which the pistons are supported. The pistons consist of a piston shaft with a piston end face and a cylindrical skirt surface moving back and forth in the cylinder bore, and a piston head supported on the swash plate.
2. Discussion of the Prior Art
Such pistons for axial piston machines are known for example from DE-A 23 20 554 and DE-A 36 09 892. At least the end regions of the cylindrical skirt surface towards the end pressure surface of these pistons are chamfered or rounded for various reasons. It is known to the skilled person that with such machines the piston play and the kinematics of such machines inevitably lead to a changing oblique positioning of the piston in the cylinder bore, which brings about increased friction and wear, in particular in the case of soft cylinder material, e.g. bronze. During the piston movement there arises at the wall of the cylinder bore a chafing effect due to the end edges of the piston/skirt surface. So that no chafing effect arises during the piston movement at the wall of the cylinder bore, the cylinder bores are in this region partially recessed. In order to reduce the wear of the walls of the cylinder, with the pistons according to DE A 23 20 554 the inner end section of the piston is bevelled towards the end pressure surface. With this configuration with bevelling (chamfering) wear still occurs in the absence of a recessing of the wall of the cylinder bore, at the entry and exit point of the piston shaft, since the bevelling has edges of its own.
It has been determined that these edges of the bevelling, or also edges chamfered with uniform, small radius of curvature, do not avoid the mentioned chafing effect. This chafing effect prevents the build up of the leakage oil lubrication film needed to discharge the heat of friction, and tends to jamming of the pistons in the cylinder bores (drawer effect).